A magnetoresistive sensor utilizing the magnetoresistive effect in which electric resistance changes depending on the change of an external magnetic field has been known as an excellent magnetic field sensor and has been put to practical use as a read element of a magnetic head which is an important part for magnetic recording and reproducing apparatus. Since size-reduction has been progressed in the magnetic storage apparatus, improvement of the performance has also been desired for a magnetic head that reads and writes information. Among them, a main objective of improving the read element includes higher areal density and higher output.
For higher recording density, narrowing of the track width and improvement of the read resolution are necessary. The track width can be narrower by narrowing a physical width, in a track width direction, of a magnetoresistive sensor film that converts a signal magnetic field generated from a magnetic recording medium into an electric signal. For this end, pattern-forming techniques including photolithography have been developed and improved.
On the other hand, the read resolution can be improved by narrowing the gap (read gap length) between two shield layers, i.e., an upper shield layer and a lower shield layer which are disposed above and below a magnetoresistive sensor film. Upon narrowing the read gap length, it is also necessary to consider the structure of the read head. In a read head of a CIP (current into plane) structure which flows a sense current in the in-plane direction of a magnetoresistive sensor film, for example, an anisotropic magnetoresistive effect (AMR) head or a giant magnetoresistive (GMR) head, insulating layers are required between a magnetoresistive sensor film and upper shield layer, and between a magnetoresistive sensor film and lower shield layer respectively so as not to leak the sense current to the shield layer and lower the output. Therefore, reducing the read gap length to about 50 nm or less is difficult. To attain the read gap length to less than that described above, a CPP (current perpendicular to plane) structure is more advantageous, in which upper and lower shield layers are used as a portion of an electrode, and a sense current flows in a direction perpendicular to the film plane of a magnetoresistive sensor film disposed between the upper and lower shield layers. The CPP structure magnetoresistive head includes, for example, a tunneling magnetoresistive effect (TMR) head and a CPP-GMR head.
However, it has been found that the CPP structure magnetoresistive head involves a problem of less dissipating heat since a portion of the magnetoresistive sensor film more tends to generate heat than the CIP structure magnetoresistive head and, in addition, the heat conduction of the shield layer is not so high as expected so far according to the inventor's study. In the CIP structure head, since the sense current flows in the in-plane direction of the stacked plane of the magnetoresistive sensor film, more sense current flows to a layer comprising a material with lower electric resistivity in the layers constituting the magnetoresistive sensor film, thus decreasing a sense current flowing to a material with high electric resistivity. Generally, the material of low electric resistivity described above is Copper provided between two ferromagnetic layers which are an important part for generating the magnetoresistive effect, and the fact that a large sense current flows in this layer means that a high output is generated. Further, a material having a high electric resistivity is a pinning layer, that is, an antiferromagnetic material or a permanent magnetic material, and decrease in the sense current flowing therethrough means that heat generation is also suppressed.
Furthermore, in the CPP structure magnetoresistive head, since the sense current flows so as to pass through the stacked plane of the magnetoresistive sensor film, an identical current flows basically to any of the layers. That is, when a large sense current flows in an intermediate layer provided between two ferromagnetic layers as an important part that generates the magnetoresistive effect, an identical current flows also to the pinning layer of high electric resistivity to result in large heat generation. In the case of a metal, since the electric resistivity increases along with temperature rise and the resistance of the read element of the CPP structure magnetoresistive head increases by the heat generation, this causes read performance deterioration such as lowering of the output or increase in resistive noises (Johnson noises). Further, since insulative films are disposed on both sides and in a stripe height direction of the magnetoresistive sensor film, which is a heat generation source, so that the sense current flows to the magnetoresistive sensor film, the heat dissipation efficiency is also poor. Such large heat generation and poor heat dissipation may result in a possibility of deteriorating a-long-time-reliability, for example, a current load lifetime.
Japanese Patent Office (JPO) Pub. Nos. JP-A-2002-151756, JP-A-2004-5763, and JP-A-2004-335071 disclose a structure of suppressing the heat generation and improving the heat dissipation efficiency of a CPP structure magnetoresistive head.
While JPO Pub. No. JP-A-2002-151756 discloses a structure in which a hard magnetic layer is adjacent to each side of a CPP stacked structural portion, it states that the hard magnetic layer in this case is a high resistance material. According to the Wiedmann-Franz law, since a material of high electric resistivity, that is, low electric conductivity also has low heat conductivity, heat dissipation efficiency is not improved.
Further, while JPO Pub. No. JP-A-2004-5763 discloses a structure of disposing a heat dissipation layer at the back in the stripe height direction of a GMR film, the heat dissipation layer is disposed through an insulating layer. Considering that the insulating layer should have such a thickness as capable of electrically insulating the GMR film and the heat dissipation layer and that the heat conductivity of the insulation material is lower compared with that of a metal, a significant advantage may not be expected even if the heat dissipation effect may be improved.
Further JPO Pub. No. JP-A-2004-335071 discloses a structure of disposing an antiferromagnetic layer of high electric resistivity so as to be in contact with the lateral side in the track width direction of the lateral side in the stripe height direction of the pinned magnetic layer and not disposing the antiferromagnetic layer in a main path of the sense current. In this structure, a sense current shunts only slightly in the anti ferromagnetic layer of high electric resistivity, and the anti ferromagnetic layer per se may generate less heat. However, since the antiferromagnetic layer is in contact with the pinned magnetic layer only on the lateral side, this structure has a less effect of pinning the magnetization of a pinned magnetic layer. Further, since the lateral side of the pinned magnetic layer is formed by an etching process, crystals of the pinned magnetic layer are damaged and/or the surface is oxidized, resulting in difficulty obtaining a sufficient magnetic coupling to pin the magnetization of the pinned magnetic layer.